Magnetron



March 11, 1958 J. s. DoNAl., JR 2,826,719

` MAGNETRON v Filed Aprill, 1955 2 Sheets-Sheet 1.

IN VEN TOR.

` Jaim wzal/Jn 7mm/EY March 11, 1958 .1. s. DONAL, JR 2,826,719

MAGNETRON Filed April 1, 1955 2 Sheets-Sheet 2 United States Patent() MAGNETRON JohnS. Donal, Jn, Princeton, N.1J.",' assignor to Rdio Corporation of America, aicorp'orationof Delaware ApplicationApril 11,t1955,fSerialfNo:r498;499 z- 16. Claims. (Cl."315;39."63)'" Ffice resonator anode cireuitof the magnetron to eliminate frequency variation de to amplitude-modulationor varia,- tion in load impedance..

Itv has been-suggested .that a magnetron be provided with`a series of radio. frequency control electrodes around the =usual` central ,cathode for establishing radio frequency controlele'ctricfields inthe part of the interaction space nearlthe cathode to lock-inthe oscillating `frequency at a desired value .duringyariation in power output. In this `arrangement,`.the two sets .of alternate control electrodes are connected tothe .two 'terminalsV of a low power radio frequency. source .of standard frequency. Experiments proved that a `magnetroncould belocked-inwith this. arrangement of control .'electrodes.-` However, a disadvantage` of this .arrangementis that, since.thercontrol.elec

trodes are in th'e. pathgof. theelectrons from the cathode mounted within' the anode block, a housing or envelope enclosing thecathode' and anode, meansfor. establishing a constant' axial magnetic' field, means for applying'a direct-current" voltage between the cathode and the anode, and' meansefor coupling"an..foutput load to" one'ofithe cavity resonators? In". operation, electrons" from` the 1- cathode are caused"'by""tliediiectlcurrent"electric and magnetic fields to 'follow"curved patlis` past" the. gaps ,betwe'enanode elements and inducehighfrequency Avoltages between theanode elements; .thus'exciting oscillations in the anode cavityresonators: The cavityresonator circuit is' capable' of `oscillating in. `a` plurality of diffrent modes each having a 'diffrent' resonantY frequency. Usually itis desired that the circuit oscillate in the so-called 1f-mode, wherein adjacent anode "elements arevr radians, Aor 180, out of phase atevery instant; Magnetrons usually'have alternate elements .strapped i together to favor 'operation iii the `wmode.` 4 4 The cavity resonator `rnagnetronfis capable of' supplying high power at ultraliighfre'quencies withhigh' efficiency; Its `geomet'ry'jand construction aresimple and straightforwardl `making the tube very attractive for Yapplicationin certainU. H. systems; However; theV systemsiwhich have found a place for 'the cavity resonator magnetronare principally' pulse'and continuous-wave systems; It is a diflicult: tubeto incorporate' into an amplitude-modulationsystembecausc otits tendency toshiftiitsoperating frequency withchangcsjin magnetron current' or load impedance.I The undesiredvariation `of magnetron frequency as a function" of magnetron'f current is 'called pushing The undesired variation in frequencyA asl a result of variation in load vimpedanceisf-called"pu1ling. The angular frequencyv of an operating cavity' resonator magnetronv can be Lwritten:

wwwa-wt.

Where wdr-:the angular resonant frequency ofi thev un loaded,-nonoperating t anodefcircuit tue-:the pushing "angular frequencyV shift due to the presence of the' electron space charge,` and wgzthe pullingangular frequency shift,1 duetto thecoupling offthe` external load to the u'anode circuit SeveraLsystems.havebeen demonstrated for. utilizing.

a cavity resonator .magnetronin anfamplitude-modulation transmitter..` using; injection-locking.' apparatus. associated with' the output line or otherwise coupled to the cavity to` the. anode, they. cause. a .deteriorating `influence f on the performance of .the tube .inthat they. interfere somewhat witlithe settingjlup (of. the yspace-charge configuration near the cathode'tthattis vitally necessary for effective control of' the oscillatingfrequency. Therefore, Aitwhasalso-been suggested that, .instead oflproviding-.radio frequency control electrodes betweenthe `cathode and the anode, .the cathode itself'be-divided.intor an annularseries of cathode elements and that the .lock-.involtage source berconnected to alternate elements-.to .produceradio frequency control voltages between adjacentcathodeelements.- The `present invention is .any` improvement. over `the two. arrangements justv described,. and.` in: some respects combines certain features thereof.

TheV principal..objecttofthe. present inventionyeisto provide more .ei'cient means forstabilizingtthe .oscillating frequency of magnetrons-,during variation infpower output.

In accordance with.. the rpresentinventom. there is. pro vided, in. .effect,..a `.anagnetrom within sa. magnetronylor. a high .power magnetron.. stabilizedwin. frequency.by allow power magnetronf built` into `the envelope .of .the larger magnetron. In.one embodimentof the invention, acens tral cathode. is. surrounded by.. anxannulartseries: oft control electrodes,. which, serve .as the.. anodefof the.I low -power control magnetronpat leastpart'of the controlelectrodes are. electron-.emissive andr serve .ast the.y cathodevfornthe surrounding main.. anodei of the.higlgiwpower` magnet-ron. The two sets offalternate ycontrol.electrodesware connected to the terminals.of.a.tuned.circuit,which.may--be acavity resonator. within the tube-envelope.r Themainmagnetron may be stabilizedin frequencyby'theactionof thecon.- trol. magnetronandits tuned-circuit alone, or the control magnetron .and its., circuit. i, mayM be-` also stabilizedff by connectionto anexternalV radio frequency sour-ceofstand-v ard frequency.. Ina modiicationzzof thetinvention,v the centraLcathodemay `be rdivided-into an annular series of cathode elements ,connected-,to `anexternal radio frequency source to. serve as .-,frequencyycontrol elements. This series of cathodeelernents mayberprovidedtwithfa cen-y tral. cathode, Ato lform..-a..still` lower :power magnetronito control. .the frequency; of lthe t lowp ower magnetron; l

In the accompanying ldrawing:

Fig. `l is` ant4 axial. sectional .-view, ftaken .1 on. line 1.-1" of Fig.1 2, of` aL vaneftype multi-cavitymagnetronembodying the presenrinvention;

Fig. 2` iswanV enlargedxfragmentary transverse-sectional view taken Online 2f.2 ofFig;` 1;

Fig.3 is .a.fragmentary axialffsectionalA view; taken ion line-3 3 of Fig.- 4,?of-,asmodiiication of` Figa 1;

Fig. .4a is anF enlarged `fragmentaryL transverse :sectional view taken on line 4-4 ofaFigSyand:

Fig.` Seis atviewvsi-rniianlto Fig.4f` of a furtherrmodication.-`

Referring, .-nowf to f the drawing-. -in-f det-ail, 'Figste 1?- anclr;2

show an` embodiment.:ofttthefrinvcntioni incorporated'in :a t

vane-type multi-cavity magnetron designed for about 1 asaeffle kw. output at a frequency of about 1000 mc. The tube structure shown comprises a main anode structure 1 including an outer cylindrical wall 3 which serves also as part of the vacuum envelope of the tube, within which are mounted in an annular array a plurality of radially extending anode vanes 5 which terminate at their inner ends or edges 5 on the surface of a cylindrical electron interaction space 7. The vanes 5 and the portions of the wall 3 between the vanes provide twelve cavity resonators 9 coupled between the inner ends 5 of the vanes S, which inner end 5 serve as anode elements of a high power magnetron. The ends of the wall 3 are hermetically closed by plates 11 and 13 which complete the vacuum envelope of the tube. The anode may be provided with conventional strapping means for favoring '1r-mode operation and/or tuning means for changing the resonant frequency of the resonator system (not shown). Apertured end plates 15 and 17 are mounted on the wall 3 adjacent to the vanes 5 to serve as end-plates for the resonators 9. A main cathode for the main anode 1, generally indicated by the reference numeral 19, is axially mounted in the interaction space 7. An axial magnetic lield is provided within the interaction space 7 by suitable means, such as the magnet poles 21 and 23. Radio frequency oscillations, generated on the anode 1 in a manner well known in the art, may be extracted from the tube by means of a coupling loop 25 and output line 27 coupled to one of the resonators 9. The structure described thus far is conventional. In normal use to generate amplitude modulated radio frequency energy, the power output of the tube would be varied by varying the anode-cathode voltage in accordance with a modulating wave. However, this would produce changes in oscillating frequency due to the phenomenon of pushing as described above. If the output load impedance is varied, changes in frequency due to pulling occur.

In accordance with the invention, the main cathode 19 is divided into an annular series of electrode elements, one for each anode element 5', which not only provide electron emission for the main auxiliary anode elements 5 but also serve-as auxliary anode elements for a central auxiliary cathode 31. In Figs. 1 and 2, only the alternate electrode elements are electron-emissive cathode elements 33, the intermediate electrode elements being non-emissive control elements 35. The main cathode 19 is shown mounted on a coaxial cavity resonator 37, which in turn is mounted by insulators 39 and 41 and screws 43 on the plate 17. The cathode elements 33, which may be coated only on the side facing the nearest anode elements 5 as shown, are mounted at one end on the inner conductor 45 of resonator 37. Each cathode element 33 may be indirectly heated by a conventional heater element (not shown) within the element, connected at one end to the element and at the other end by a heater lead 47 to a heater terminal ring 49 insulatedly mounted on the resonator 37. Heater current may be fed to the heater means of cathode lead 51 and heater lead 53 extending through the envelope and connected to a heater source 55. The non-emissive control elements 35 are provided at the ends with offset portions 57 and 59 connected, respectively, to a ring 61 and the outer conductor 63 of the resonator 37. The auxiliary cathode 31 is axially mounted in the space defined by the electrode elements 33 and 35, as by means of a tubular extension 67 and a support plate 69 mounted in insulated relation on the resonator 37. The cathode 31 is provided with an internal heater (not shown) and leads 71 and 73 extending through the envelope for connection to a heater voltage source 74. Preferably, the inner conductor 45 is provided with a tubular re-entrant extension 75 for shielding the heater leads 47 from the cathode extension 67, as shown.

In operation, the main anode 1 and main cathode 19 constitute a rst or main magnetron for generating and delivering relatively high power radio frequency energy to a load. The cathode elements 33 and control elements phase.

35 constitute the anode of a low power second or auxiliary magnetron having auxiliary cathode 31 as the cathode for controlling or stabilizing the oscillating frequency of the first or high power magnetron. In operation of the magnetron as an amplitude-modulated oscillator, a direct-current voltage source 79 is connected between the resonator 37 and the anode 1, to establish the cathodeanode voltage on the high power magnetron. A directcurrent voltage source 77 is connected between the lead 73 for the auxiliary cathode 31 and the lead 51 for the resonator 37, to establish the cathode-anode voltage on the control magnetron. The magnetron may be amplitude-modulated by connecting an amplitude modulated source 81 in series with the source 79 to vary the cathodeanode voltage of the power magnetron. Instead, the cathode elements 33 and control elements 35 may be insulated from each other and the amplitude-modulating signal be applied thereto as a low frequency voltage therebetween.

The resonator 37 is so connected to the electrode elements 33 and 35 as to cause 1r-mode operation of the control magnetron in which adjacent elements are out of phase at any instant. The control magnetron generates radio frequency oscillations on the main cathode 19, by establishing control voltages of desired frequency between adjacent electrode elements 33 and 35, which in turn stabilize the oscillating frequency of the main or power magnetron at that frequency, or some harmonic frequency. By use of this arrangement the frequency of a relatively large magnetron delivering power to a load can be stabilized to a great extent during variation in power output without the necessity of an external radio frequency source. If desired, means can be provided for tuning the resonator 37 to dilerent frequencies.

In some cases, the amount of pushing or pulling may be so great that the frequency cannot be stabilized sufficiently by the operation of the independent control magnetron by itself. In such cases, the control magnetron may itself be stabilized, as by coupling the resonator 37, by means of a coupling loop 83 and transmission line 85, to an external radio frequency source (not shown).

Figs. 3 and 4 show a modification of Figs. 1 and 2 in which all of the control elements of the magnetron are electron emissive cathode elements 33a and 33b constituting the main cathode. Alternate cathode elements 33a are mounted on the inner conductor 45 of resonator 37 as in Figs. 1 and 2. The intermediate cathode elements 33b are mounted on arms 63h which extend inwardly from the outer conductor 63 through slots 45a in the inner conductor 45. Thus, the two sets of alternate elements 33 are connected to the two terminals of the resonators, so that adjacent elements will operate 180 out of The remaining structure and the method of operation of Figs. 3 and 4 are the same as in Figs. l and 2, except that it would not be practical to amplitude modulate the magnetron of Figs. 3 and 4 by applying the amplitude modulating signal between adjacent cathode elements.

Fig. 5 shows a modification of Figs. 3 and 4 in which the auxiliary inner cathode is also divided into an annular series of cathode elements 86, which may be similar to but smaller than #the elements 33 of Figs. 1-4. The cathode elements 33a and 331: constituting the main cathode of the power magnetron may be mounted at one end (not shown) in the same manner as in Figs. 3 and 4. The'inner cathode elements 86` may be mounted by means (not shown) similar Ito the mounting means for cathode elements 33a and 33b, which may include a second control resonator resonant at a frequency that is a harmonic of the operating frequency. In operation of Fig. 5, radio-frequency control voltages are applied by suitable means (not shown) between adjacent cathode elements 86 to stabilize Vthe oscillating frequency of the control magnetron, which in turn stabilizes the oscillating frequency of the high power magnetron. In this arrangement the resonator 37 would not be separately excited.

It will be understood that the cathode elements 86 of Fig. 5 could also be used in place of the auxiliary cathode 31 in the embodiment shown in Figs. 1 and 2. Moreover, the elements 86 could be alternately emitting and non-emitting, like the elements 33 and 35 of Figs. 1 and 2.

What is claimed is:

1. A magnetron structure including: a main magnetron comprising a main anode, and means including a main cathode adjacent to said main anode for generating radio frequency oscillations on said anode; and an aux iliary magnetron comprising said main cathode as an auxiliary anode, and means including an auxiliary cathode adjacent to said main cathode on the side thereof opposite to said main anode for generating radio frequency oscillations on said main cathode, to control said oscillations on said main anode.

2. A magnetron structure including: a main magnetron comprising a hollow cylindrical main anode including at least one cavity resonator, and means including a hollow cylindrical array of electrode elements, at least part of which are electron-emissive, coaxially mounted within said main anode; and an auxiliary magnetron comprising said array of electrode elements as an auxiliary anode, and means including an auxiliary cathode coaxially mounted within said array- `of electrode elements.

3. A magnetron structure as in claim 2, wherein said auxiliary cathode comprises a hollow cylindrical array of electrode elements, at least part of which are electronemissive.

4. A magnetron comprising: a main anode, a main cathode adjacent to said anode, means for establishing a magnetic eld normal to the paths vof electrons from said cathode to said anode, means for establishing a first direct-current potential diierence between said cathode and said anode, for generating radio frequency oscillations on said main anode, and means for varying the amplitude of said oscillations; and an auxiliary cathode adjacent to said main cathode and means for establishing a second direct-current potential difference between said auxiliary cathode and said main cathode, for generating radio frequency oscillations on said main cathode to stabilize the frequency of said oscillations on said main anode during said amplitude variation; said main cathode being located between said auxiliary cathode and said main anode.

5. A magnetron comprising: ya hollow main anode, a hollow main cathode mounted within said anode, means for establishing an axial magnetic field within said anode, and means for establishing a first direct-current potential diierence between said cathode and said anode, for generating radio frequency oscillations on said anode; and an auxiliary cathode mounted within said main cathode and means for establishing a second direct-current potential diiferencebetween said auxiliary cathode and said main cathode, for generating radio frequency oscillations on said main cathode to control said oscillations on said main anode.

6. A magnetron including a hollow main anode comprising an annular array of spaced main anode elements defining an interaction space, a `resonant anode circuit coupled between adjacent anode elements, means for establishing an axial magnetic field within said space, an auxiliary cathode coaxially mounted in said space, and an anode for said auxiliary cathode comprising an annular array of spaced auxiliary anode elements interposed between said auxiliary cathode and said main anode elements, at least part of said auxiliary anode elements being electron-emissive and adapted to serve as the cathode for said main anode.

7. A magnetron as in claim 6, wherein said anode circuit comprises at least one cavity resonator connected between adjacent main anode elements.

8. A magnetron as in claim 6, wherein the number of said auxiliary anode elements is the same as the number of main `anode elements.

9. A magnetron as in claim 8, wherein each of said auxiliary anode elements is located opposite the midpoint of the gap between two adjacent main anode elements to minimize electrostatic coupling therebetween.

10. A magnetron including a hollow anode compris ing `an annular array of spaced anode elements deiining an interaction space, a resonant anode circuit coupled between adjacent anode elements, means for establishing an axial magnetic field within said space, a cathode coaxially mounted in said space, an electrode structure comprising an annular array of spaced control elements interposed between said cathode and said anode elements, at least part yof said control elements being electron-emissive, and a resonant circuit coupled between adjacent control elements.

11. A magnetron as in claim 10, wherein said resonant circuit comprises a cavity resonator located within the vac-num envelope of the magnetron.

12. A magnetron as in claim 11, including means for coupling said cavity resonator to an external source of radio frequency control volt-age.

13. A magnetron including a 4hollow anode comprising an annular array of spaced anode elements defining an interaction space, a resonant anode circuit coupled between adjacent anode elements, means for establishing an axial magnetic iield within said space, a cathode coaxially mounted in said space, and an electrode structure comprising an annular array of spaced control elements spaced interposed between said cathode and said anode elements, alternate ones of said control elements being electron-emissive and the other control elements being non-emissive.

14. A magnetron including a hollow main anode comprising an annular array of spaced anode elements dening an interaction space, a resonant anode circuit coupled between said adjacent anode elements, means for establishing an axial magnetic field within said space, an

auxiliary cathode coaxially mounted in said space, and an electrode structure comprising an annular array of spaced electron-emissive control elements interposed between said `auxiliary cathode and said anode elements and adapted to serve as the cathode for said main anode and also as the anode tfor said auxiliary cathode.

15. A magnetron as in claim 6, wherein said auxiliary cathode is a single cylindrical electron-emissive element.

16. A magnetron as in claim 6, wherein said auxiliary cathode comprises an annular array of elements, at least part of which are electron-emissive, adapted to be excited to establish radio frequency control voltages between adjacent cathode elements for locking-in the frequency of said magnetron.

References Cited in the file of this patent UNITED STATES PATENTS 2,467,538 Shoupp Apr. 19, 1949 2,624,863 Clogston Ian. 6, 1953 2,782,342 Kilgore Feb. 19, 1957 FOREIGN PATENTS 641,086 Great Britain Aug. 2, 1950 

